If other sets in the house are fine, then it's probably either the cable between the source(cable or satellite) and the television, or equipment at the set (cable/satellite box, vcr)
If you have a cable set top box or a satellite receiver and get a fuzzy picture the problem is most likely with the connection between the box and the TV.
There is a problem with the signals getting to the tv. You may have a loose connection or bad wireing. Check the connections between the cable wiring and the outlet or box. If that dosnt work, try replacing the cable wire on that tv.
After the DTV switch did you upgrade that TV with a digital converter box? If so, then it could be simply that the TV is located in an area of the house that doesn't receive a good signal. You could try installing a larger antenna.
The channels are fuzzy only on one TV for an easier view. If each channels are in different TVS the access to it will be difficult. The easier view is possibel if it is in on TV, as it requires only pressing of some buttons. The usage of power can also be limited.
